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Current Otolaryngology > I. Introduction > Chapter 4. Anesthesia for Head & Neck Surgery >
| Anesthetic Drugs In head and neck surgery, anesthetists use a number of drugs in monitored conditions. These drugs may be used in procedures requiring conscious sedation. Although a large majority of office-based procedures are accomplished with the use of conscious sedation, a number of procedures performed at same-day surgery centers are also done with conscious sedation. Analgesics, Sedatives, & Hypnotics Opioids General Considerations Opioids mediate analgesia through a complex interaction of opioid receptors in the supraspinal central nervous system (CNS). They produce reliable analgesia as well as provide some sedation and euphoria. There is no impairment of myocardial contractility, but sympathetically mediated vascular tone is reduced. Ventilation is depressed because of elevation of the carbon dioxide threshold for respiration. Opioids given at recommended doses do not reliably produce unconsciousness. They may, however, cause decreased bowel motility , biliary spasm, nausea, and pruritus. Routes of Administration Opioids may be given by intermittent intravenous or intramuscular routes. Plasma level peaks and valleys may lead either to variations in the desired analgesia or excessive side effects. Continuous infusions or patient-controlled analgesia with smaller, more frequent doses has been shown to lead to better analgesia, with fewer side effects and less total drug use. Fentanyl and morphine may also be administered by an intrathecal or an epidural route. Either of these administration routes allows the placement of opioids in the vicinity of spinal cord receptors. A growing body of information supports the use of these routes in high-risk patients to provide superior analgesia, less sedation, and less decrement in pulmonary function. Drug Tolerance Tolerance developed by the induction of hepatic microsomal enzymes may occur over the course of days or weeks. The narcotic effects may be reversed with a variety of antagonists (eg, naloxone). Acute reversal may be accompanied by agitation, pulmonary and systemic hypertension, and pulmonary edema. Morphine Morphine is relatively hydrophilic and thus has a slow onset with a fairly long clinical effect. Only a small amount of administered morphine gains access to the CNS, but it accumulates rapidly in the kidneys, liver, and skeletal muscles . Profound vein vasodilatation may be induced owing to the effects of histamine release and the reduction of sympathetic nervous system tone. Fentanyl A synthetic opioid, fentanyl has effects similar to morphine but it is more lipid soluble, has a more rapid onset, and has a shorter duration of action. These factors contribute to faster entrance into the CNS and the prompt redistribution away from the CNS. Elevated doses may lead to progressive saturation in adipose tissues. When this occurs, plasma concentrations do not decline promptly. Thus, pharmacodynamic effects, including ventilatory depression, may be prolonged. Remifentanil Remifentanil was recently introduced and has a much more rapid onset and offset than fentanyl. With the initial dose, anesthesia may be achieved in approximately 3060 seconds; the offset of the drug can occur within 510 minutes after the infusion is discontinued. Because remifentanil is metabolized in blood and skeletal muscle, it can be administered as a single dose or in an infusion. Because of the potency of this opioid and because chest wall rigidity may result, this drug should be administered by an anesthesiologist or an anesthetist. Meperidine Commonly known as Demerol, meperidine has one tenth the potency of morphine and a shorter duration of action. In low doses it has been shown to decrease the shivering associated with rewarming after surgery and after amphotericin B administration. Several metabolites are excreted by the kidney and may accumulate in the presence of renal disease. The major metabolite, normeperidine, is a proconvulsant and may cause seizures in patients with renal insufficiency. Benzodiazepines General Considerations Benzodiazepines produce anxiolysis and sedation by facilitation of the inhibitory actions of GABA on nerve conduction in the cerebral cortex . They may be used to produce sedation and amnesia, facilitate patient cooperation, attenuate alcohol withdrawal syndrome, treat seizures, and relieve muscle spasm. Benzodiazepines have no analgesic properties. They may cause transient decreases in blood pressure due to decreased catecholamine levels and systemic vascular resistance, but with little effect on contractility. Respiratory depression is usually minimal and well tolerated in clinical doses, but it may be accentuated in the elderly and patients with chronic obstructive pulmonary disease. Titration to a cooperative, oriented, and tranquil state (level 2 on the Ramsey Scale) is the desired effect. Patients with a history of heavy alcohol or sedative use may require considerably more drug to achieve this response. Diazepam, midazolam, and lorazepam are three of the more commonly used benzodiazepines. Drug Tolerance Tolerance to benzodiazepines develops in a manner similar to prolonged alcohol and opiate use. Withdrawal may result in profound sympathetic autonomic response. The replacement of benzodiazepine plasma levels and transient autonomic control would be indicated for the control of withdrawal symptoms. Sedation Reversal The reversal of benzodiazepine-induced sedation has been reported with physostigmine and aminophylline. Flumazenil, a specific benzodiazepine-receptor antagonist, provides a consistent reversal of sedation within 2 minutes of intravenous administration. The duration of reversal is short; therefore, resedation is a possibility in cases of benzodiazepine overdose. Flumazenil has also been reported to transiently reverse the somnolence of hepatic encephalopathy. Therapy with this agent should be gradual to avoid excitatory symptoms. Convulsions have been reported in patients who are seizure prone and benzodiazepine dependent. Diazepam Diazepam has a long clinical duration because of the long half-life of several active metabolites. It is not water soluble, and the parenteral suspension of propylene glycol is irritating when given intravenously or intramuscularly. Because diazepam requires microsomal nonconjugative pathways for degradation and elimination , it should not be administered to patients with acute hepatitis. Midazolam Midazolam is the most commonly used benzodiazepine in the intensive care unit. It is water soluble, with short clinical duration, and it has fewer active metabolites. Midazolam offers a more rapid onset and a greater degree of amnesia than other benzodiazepines, which makes it a good choice for brief procedures such as esophagogastroduodenoscopy (EGD) and bronchoscopy. Lorazepam Lorazepam is another frequently used long-acting benzodiazepine. There is no pain on injection and no active metabolites. This agent has become a popular choice for patients with liver disease because its metabolism is not dependent on microsomal enzymes. Alpha 2 -Agonist The  2 -agonist dexmedetomidine is a class of sedative drug that has been approved by the FDA for use as a sedative and analgesic in the operating room and in the intensive care unit. Dexmedetomidine has pharmacologic actions similar to those of clonidine except that its affinity for the 2 -receptor is eight times greater, making dexmedetomidine five to ten times more potent than clonidine. In the past few years , the use of dexmedetomidine for the management of sedation and analgesia in the perioperative setting has increased significantly. Dexmedetomidine also possesses several properties that may additionally benefit postoperative patients who have an opioid tolerance or who are sensitive to opioid-induced respiratory depression. In spontaneously breathing volunteers, intravenous dexmedetomidine caused marked sedation with only mild reductions in resting ventilation at higher doses. Head and neck surgeons will find this drug useful for conscious sedation cases, augmented sleep studies, and fiberoptic intubations and tracheostomy placement. Dexmedetomidine does cause some cardiovascular instability, which can be avoided when the drug is titrated carefully . Nevertheless, it should be appreciated that dexmedetomidine does cause some moderate reductions in blood pressure and heart rate. Anesthesia Induction Drugs Injected Anesthetics Barbiturates Once a mainstay in sedation management, barbiturates now seem to have fallen out of favor, mainly because of the availability of more titratable alternatives. They have numerous sites of action, but they most likely promote the inhibitory effects of GABA on neuronal function. They have no analgesic effect and cause dose- related CNS, cardiac , and respiratory depression. Short-acting agents such as methohexital and thiopental sodium are useful to produce unconsciousness for very short procedures, such as cardioversions and intubations. Both agents also can be used for short- term procedures such as examining the oropharynx of a noncooperative patient. As with most anesthetic induction drugs, patients should be adequately monitored (ie, heart rate, blood pressure, electrocardiogram, and pulse oximetry), and supplemental oxygen should be given. Emergency endotracheal intubation equipment should be readily available together with emergency medications. Dosage measures must be judicious because of the increased likelihood of respiratory and hemodynamic depression, especially in elderly patients. Both medium-acting agents (eg, pentobarbital IV/PO) and long-acting agents (eg, phenobarbital PO) have been used for violent agitation refractory to other agents, status epilepticus, and the induction of barbiturate coma to treat increased intracranial pressure. Propofol Propofol is an ultra -short-acting intravenous anesthetic agent. Unconsciousness may be induced in less than 30 seconds followed by awakening in 48 minutes. It has potent sedative hypnotic activity, but unlike with other agents, awakening is markedly rapid from even deep sedation, with minimal residual sedative effects and good antiemetic qualities. The hepatic metabolism of propofol is rapid, but rapid redistribution also plays a role in early awakening. It has no pharmacologic active metabolites. Propofol has been shown to decrease systemic blood pressure as a result of myocardial depression and vasodilatation. When used in low doses (eg, 1050 mcg/kg/min) as a continuous infusion for sedation, these effects are minimal. Propofol has no analgesic effects but has been shown to decrease narcotic requirements. One of the disadvantages in using this agent is that propofol is only slightly water soluble. It must be formulated in an oil and water emulsion of soybean oil, egg lecithin, and glycerol. This formulation is similar to a 10% intralipid solution. Thus, this agent is contraindicated in patients with the potential for allergic responses to the emulsion components . Pain is common on injection but often can be attenuated by pretreatment of the vein with a 20- to 40-mg lidocaine bolus before infusion. With prolonged used, blood lipid levels should be assessed to rule out hypertriglyceridemia. Propofol should be treated with the same degree of caution as parenteral nutrition solutions. Multiple reports of bacterial contamination due to manipulations of the emulsion medium demonstrate that it supports rapid bacterial growth. Recent formulations of propofol have included bacteriostatic agents such as EDTA or sulfites, which have made this issue less of a clinical concern. Nonetheless, clinical guidelines still limit the handling of opened vials to less than 24 hours and, when used as an infusion, advocate line changes at regular (usually 12- hour ) intervals. A soluble cousin of propofol marketed as Aquavan (fospropofol disodium) is undergoing phase III studies and should be available for use in 2007. The drug is described to have similar properties as propofol without the pain experienced during injection. The drug has been used for conscious sedation for colonoscopies with success in several phase III studies. Like propofol, Aquavan can also cause respiratory depression and hence should be used with care and in a monitored setting with emergency airway equipment. Ketamine Ketamine is a phencyclidine derivative (similar to LSD) that produces a docile, dissociative state that may be exploited as a sedative. Agitated patients may be given an IM injection of 35 mg/kg or a titration of 10-mg intravenous boluses to produce a cataleptic state in which the eyes remain open with a slow nystagmic gaze. Amnesia is present and analgesia is intense . The additional advantages of using ketamine include the maintenance of airway reflexes, cardiovascular stimulation, and bronchial relaxation. The disadvantages include increased airway secretions, transient increases in intracranial pressure, and associated unpleasant visual or auditory illusions. The addition of benzodiazepines may attenuate some of these untoward sensory effects. Examples of the clinical utility of this drug include conscious sedation for burn wound dressing changes and facilitating endotracheal intubation in the hypotensive patient. Inhaled Anesthetics In the operating room, general anesthesia is commonly maintained with inhaled anesthetics. These agents also provide some analgesia, amnesia, and muscle relaxation. In pediatric patients in whom there is no intravenous access, anesthesia may be induced by inhalation. All of the inhaled anesthetics, with the exception of nitrous oxide, are bronchodilators and may be useful in patients with reactive airways. Most inhaled agents reduce blood pressure owing to either direct cardiac depression (eg, halothane) or vasodilation (eg, isoflurane, sevoflurane, or desflurane). The rapidity of anesthetic induction as well as emergence from anesthesia is based on the lipid solubility characteristics of the inhaled anesthetic. The more insoluble the anesthetic agent, the faster the induction of anesthesia. The agents with high lipid solubility prolong the emergence from anesthesia. Nitrous Oxide Nitrous oxide produces general anesthesia through interaction with the cellular membranes of the CNS. Nitrous oxide is the only nonorganic inhaled anesthetic in clinical use. Although it is nonvolatile, it does support combustion and caution should be taken in the event of airway fires. The uptake and elimination of nitrous oxide are relatively rapid compared with other inhaled anesthetics and are primarily the results of its low blood-gas partition coefficient. It produces analgesia, amnesia (with a concentration greater than 60%), mild myocardial depression, and mild sympathetic nervous system stimulation. It does not significantly affect heart rate or blood pressure. Nitrous oxide is a mild respiratory depressant, although less so than the volatile anesthetics. The elimination of nitrous oxide is via exhalation. Isoflurane Until recently, isoflurane was the most commonly used inhaled anesthetic in the United States. Isoflurane causes minimal cardiac depression. Like other volatile anesthetics, isoflurane causes respiratory depression with a decrease in minute ventilation. The ventilatory response to hypoxia and hypercapnia is diminished. Another characteristic that isoflurane shares with other volatile anesthetics is its ability to cause bronchodilation; this effect occurs despite its ability to cause airway irritation. Isoflurane increases skeletal muscle blood flow, decreases systemic vascular resistance, and lowers arterial blood pressure. High concentrations of isoflurane may increase cerebral blood flow and intracranial pressure. These effects are effectively reduced by hyperventilation. At even higher concentrations, isoflurane reduces cerebral metabolic oxygen requirements and provides cerebral protection. It also decreases renal blood flow, glomerular filtration rate, and urinary output. Desflurane The structure of desflurane is very similar to that of isoflurane except for the substitution of a fluorine atom for a chlorine atom. This composition makes desflurane highly insoluble. Its low solubility in blood and body tissues causes a very rapid "wash-in" and "wash-out" of the gas. The time required for patients to awaken is approximately half as long as that observed following isoflurane administration. Desflurane has cardiovascular and cerebral effects similar to those of isoflurane. Sevoflurane Sevoflurane has begun to replace halothane as a primary inhaled anesthetic agent used in anesthesia induction when an intravenous induction cannot be performed. It is used primarily in pediatrics where intravenous access is not available and induction has to be achieved by other means. Nonpungency and a rapid increase in alveolar anesthetic concentration make it an excellent choice for smooth and rapid inhalation induction of anesthesia. The blood solubility of sevoflurane is slightly greater than that of desflurane. Sevoflurane mildly depresses myocardial contractility and systemic vascular resistance and arterial blood pressure decline slightly less than with isoflurane or desflurane. As with isoflurane and desflurane, sevoflurane causes slight increases in cerebral blood flow and intracranial pressure at normocarbia. Sevoflurane is reported to have potential for nephrotoxicity and therefore should be used with a gas flow of > 2 L. Halothane Halothane is a halogenated alkane that is used primarily for inducing anesthesia in patients when an intravenous induction is not possible. The nonpungent and sweet-smelling odor of halothane makes it especially suitable for this purpose. Halothane causes a dose-depression reduction in arterial pressure by myocardial depression. It also causes respiratory depression. This anesthetic drug has been associated with a drug-induced hepatitis known as halothane hepatitis. This condition is extremely rare, with an incidence of 1 in 35,000 patients. The risk of halothane hepatitis is increased in (1) patients exposed to multiple doses of halothane anesthesia within short intervals, (2) middle-aged obese women, and (3) patients with a genetic predisposition to halothane hepatitis. Antiemetics Droperidol Droperidol has greater antiemetic and sedative effects than other anesthetic agents, but it may also produce respiratory depression. If administered alone, dysphoria can result; at clinical doses, it is used in combination with a narcotic or benzodiazepine for sedation. More recently, the FDA has discouraged the use of droperidol in unmonitored settings. Ondansetron & Dolasetron Ondansetron and dolasetron are selective antagonists of serotonin 5-HT 3 receptors with little or no effect on dopamine receptors. Unlike droperidol, they do not cause sedation, extrapyramidal signs, or alterations of GI motility and lower esophageal sphincter tone. 5-HT 3 receptors are found in the chemoreceptor trigger zone of the area postrema, in the nucleus tractus solitarius, and also along the gastrointestinal tract . The most common reported side effect is headache . Dolasetron can also prolong the QT interval. Neuromuscular Blockers Neuromuscular blocking agents are used most commonly for facilitation of endotracheal intubation and in the operating room when patient movement is detrimental to the surgical procedure. The clinical pharmacology of the most frequently used neuromuscular blocking agents can be found in Table 41. The most prominent side effect of neuromuscular blockers is that they cause paralysis of the respiratory muscles. Hence, patient ventilation must be ensured by the anesthesiologist and can be achieved with a mask or a secured endotracheal tube. | Table 41. Pharmacokinetics of the More Commonly Used Neuromuscular Blockers. Only Vecuronium Is Used as an Infusion.
| | | Agent | Intubation Dose | Time to Onset | Time to Recovery | Infusion Rate | | Vecuronium | 0.1 mg/kg | 23 minutes | 2530 minutes | 12 mcg/kg/min | | Cisatracurium | 0.2 mg/kg | 12 minutes | 5060 minutes | --- | | Pancuronium | 0.1 mg/kg | 5 minutes | 80100 minutes | --- | | Rocuronium | 1.2 mg/kg | 12 minutes | 40150 minutes | --- | |
| Most muscle relaxants induce paralysis by blocking acetylcholine receptors at the neuromuscular junction of skeletal muscle. They have no intrinsic sedative or analgesic properties and must be used in concert with other medications. At a minimum, these agents should be used in conjunction with an anxiolysis agent. Inadequate sedation and hypnosis while using neuromuscular blockers can produce unpleasant recall by patients, with long-term side effects. Vecuronium Vecuronium is a relaxant that is popular because of its short clinical duration (3060 minutes) and lack of hemodynamic side effects. It may be given as a bolus or as a continuous infusion. It is metabolized by the liver and excreted by the kidneys. Cisatracurium Cisatracurium undergoes degradation in plasma at physiologic pH and temperature by organ-independent Hofmann elimination. Metabolism and elimination appear to be independent of renal or liver failure. It does not affect heart rate or blood pressure nor does it produce autonomic effects. Pancuronium Pancuronium has a longer duration of action (6090 minutes) and is eliminated primarily by renal mechanisms. The major limiting factor of its use is the side effect of tachycardia, which results from a vagolytic effect, especially after bolus administration. Rocuronium Rocuronium has an onset of action similar to but slightly longer than that of succinylcholine, making it suitable for rapid-sequence inductions; however, the duration of action is much longer. This intermediate duration of action is comparable to that of vecuronium. Rocuronium undergoes no metabolism and it is eliminated primarily by the liver and slightly by the kidneys; its duration of action is modestly prolonged by severe hepatic failure and pregnancy . | | Other Drugs of Value to the Otolaryngologist Ketorolac Ketorolac is a recently released potent parenteral nonsteroidal analgesic without opioid-related side effects such as respiratory depression. An intramuscular dose of 60 mg is reported to be equivalent to a morphine dose of 10 mg for up to 3 hours. Clinical dosing is every 8 hours, and it appears to be the most effective in situations where swelling contributes to pain (ie, dental, gynecologic, and orthopedic surgery). It has minimal impact on ventilation, hemodynamics, and bowel motility. The disadvantages of its use include a limited analgesic effect beyond the recommended doses and an impaired platelet function. Substantial gastrointestinal mucosal breakdown may occur with use over a period as short as 1 week. Anticholinergic Agents Anticholinergic agents are sometimes used to produce sedation and amnesia. They also have an antisialagogue effect and prevent reflex bradycardia. Atropine and scopolamine are tertiary amines that cross the lipid barrier protecting the CNS. In terms of centrally induced sedation and amnesia, scopolamine has 10 times the potency of atropine. Because scopolamine produces tachycardia as its major hemodynamic side effect, it is a popular choice as an urgent amnestic agent for the hemodynamically unstable or hypovolemic patient (eg, a trauma victim). Undesirable side effects include (1) toxic delirium (known as central cholinergic syndrome), (2) tachycardia, (3) the relaxation of lower esophageal sphincter tone (with the associated potential for regurgitation), (4) mydriasis, and (5) the potential elevation of temperature via suppression of sweat gland function. | | Anesthetic Equipment The basic equipment for airway management used by the anesthesiologist should be familiar to the otolaryngologist. This equipment includes laryngoscope blades, endotracheal tubes, and breathing circuits. Laryngoscope Blades In general, laryngoscope blades may be classified as either straight or curved . With proper head positioning, both types of blades provide a direct pathway to the vocal cords for endotracheal intubation. There are several designs of laryngoscope blades as shown in Figure 41. Some blades, like the Bainton blade , may be used in special situations in which redundant tissue or airway edema is present and the vocal cords are not easily visible. Endotracheal Tubes Otolaryngologists often require specialized endotracheal tubes, depending on the procedure performed. The standard endotracheal tub e is m ade of polyvinyl chloride and is disposable. It can be made of clear silicon. Reusable rubber tubes are also available; these tubes have to be cleaned and autoclaved before reuse. Endotracheal tubes come in various sizes and may be cuffed or uncuffed. Uncuffed endotracheal tubes are used in neonates, infants, and children usually up to the age of 12 years. Suggestions for tube sizes in children are shown in Table 42. The tracheal end is usually beveled and may contain a Murphy eye. Endotracheal tube cuffs may be either high volume or low volume; both types of cuffs may cause tracheal necrosis with long-term intubation. Endotracheal tubes have gradations, usually in centimeters, to allow the clinician to keep track of the correct position of the tube and to prevent endobronchial migration or extubation. For common procedures of the larynx, the use of a small-diameter endotracheal tube allows for better exposure. The recommended size is 5.0 mm ID for women and 5.5 mm ID for men. | Table 42. Recommended Endotracheal Tube Sizes for Pediatrics.
| | | Patient Age | Patient Weight | Cuff Size | Cuff Length | | < 1 month | 24 kg | 2.53.5 mm | 1012 cm | | 16 months | 46 kg | 4.04.5 mm (uncuffed) | 1214 cm | | 612 months | 610 kg | 4.55.0 mm (uncuffed) | 1416 cm | | 13 years | 1015 kg | 5.05.5 mm (uncuffed) | 1618 cm | | 46 years | 1520 kg | 5.56.5 mm (uncuffed) | 1820 cm | | 710 years | 2535 kg | 6.57.0 mm (uncuffed) | 2022 cm | | 1014 years | 4050 kg | 7.07.5 mm (cuffed) | 2224 cm | |
| For a variety of head and neck procedures, specially designed endotracheal tubes may be required. These tubes are designed to provide optimal exposure for the surgeon working in the oral and nasal cavities. The anatomic design of these tubes prevents their kinking during surgery. Classification of Endotracheal Tubes Three of the more commonly used endotracheal tubes are RAE endotracheal tubes, armored endotracheal tubes, and laser-resistant endotracheal tubes (Figure 42). These tubes are commonly used for head and neck surgery. RAE Endotracheal Tubes RAE endotracheal tubes, named after the inventors of the tube (Ring, Adair, and Elwyn), have a preformed shape to fit the mouth or nose. The tubes are available in a variety of pediatric and adult sizes and may be cuffed or uncuffed. Nasal RAE tubes are commonly used in surgery of the oral cavity, since they do not obstruct the surgical field. Oral RAE tubes are commonly used for surgeries of the oral cavity, particularly those involving the tonsils. A drawback to RAE tubes use is that their shape may result in an inadvertent endobronchial intubation, particularly in patients with short necks. Armored Endotracheal Tubes Armored endotracheal tubes are commonly used in head and neck surgery. The primary advantage of using these tubes is that they can withstand the constant moving of the head without kinking. Laser-Resistant Endotracheal Tubes Laser-resistant endotracheal tubes are used in laser surgery (eg, in the treatment of vocal cord papillomas). Regular endotracheal tubes can be converted to laser-resistant tubes by wrapping the ends with aluminum foil. Breathing Circuits After an airway is secured, oxygen is provided to the patient either (1) via a ventilator in the operating room and the intensive care unit or (2) manually, by a breathing circuit connected to an oxygen tank. The otolaryngologist should understand the components of a breathing circuit commonly used both for transporting ventilated patients and in office-based practice. The most common breathing circuit used for adults is the Mapelson F or Jackson-Rees circuit. The circuit contains a reservoir bag with a valve, a corrugated circuit, and a fresh gas flow near the attachment to the mask or the endotracheal tube (Figure 43). This device is used for manual ventilation either by a mask or by an endotracheal tube. This circuit can also be used to ventilate patients in emergency situations, when a ventilator is unavailable. | | Airway Management A high percentage of cases involving the head and neck involve patients with "difficult airways." A patient with a difficult airway may pose a challenge for both manual ventilation and the placement of an endotracheal tube. Patients with difficult airways should be identified prior to surgery, especially before the induction of general anesthesia; in particular, these patients should be identified before neuromuscular blockers are used. Preoperative evaluation by the otolaryngologist, either by directly viewing the airway or by other diagnostic tools such as a CT scan or MRI, may provide invaluable information to the anesthesiologist, particularly if a difficult airway is involved. Identification of Potential Airway Problems With improvements both in record keeping and communications between patient and physician, the patient history should provide important information about the patient's airway and any potential problems for securing the airway in the operating room. Knowledge of a history of difficult intubation, prior head and neck surgery, the immobility of cervical vertebrae, and radiation therapy to the airway should alert the physician about a potentially difficult airway. Other alert items should include dysphagia, trauma to the head and neck, hoarseness, and stridor (Table 43). | Table 43. Conditions that May Help the Physician Identify Patients with Potential Airway Difficulties.
| | | Prior difficulty with endotracheal intubation | | Cervical immobility (limited or no range of neck motion) | | Hoarseness or stridor | | Trauma | | Radiation therapy | | Prior surgery of the head, neck, or both | | Morbid obesity | | Dyspnea or dyspnea on exertion | | Dysphagia | | Shortness of breath | |
| Physical Examination In most cases involving head and neck surgery, a detailed preoperative assessment of the airway may be performed by the otolaryngologist. This assessment is extremely helpful in determining which patients may have difficulties with endotracheal intubation. The preoperative exam should therefore include (1) a detailed frontal and profile view to assess mandibular size and mobility; (2) an examination and assessment of the mental-alveolar process and either the mental-hyoid bone or the mental- thyroid cartilage distance; (3) an assessment of neck rotation and flexion-extension mobility; and (4) an examination of the neck for evidence of masses, tracheal deviation, the size of tracheal and cricoid cartilage, and tissue plasticity. Carefully assessing patient breathing patterns and phonation may also provide the physician with important clues about airway patency and potential difficulties with endotracheal intubation (Figure 44).
An intraoral examination also should be performed as part of the preoperative assessment. It should include an assessment of tongue size, protrusive occlusion , and the degree of overbite (Table 44). Examining the oral cavity and assessing the structures that can be seen when the patient's mouth is opened wide can assist the physician in recognizing a potentially difficult airway. The classification of these views is called the Mallampati classification (Figure 45). In about 80% of oral (Mallampati) Class I views, a Grade 1 laryngoscopic view is observed. For Mallampati Class II, only the posterior vocal cords may be visualized in about 50% of cases. Class III and IV merit special attention as intubation of the trachea in these patients may be difficult and may indicate intubating patients while they are awake. The degree of vigilance should also be increased for patients in Classes III and IV, since manual ventilation may be a challenge. | Table 44. an Intraoral Examination Can Provide Important Information Regarding Potential Airway Difficulties.
| | | Loose, missing, or overly large teeth | | Degree of overbite or protrusive occlusion | | Size of the tongue | | Visibility and size of facial structures | | Patency and size of the nares; deviation of nasal septum | |
| Intubation of the Conscious Patient Patient Preparation In patients with anticipated difficult airways or patients who are unable to either open their mouths or have cervical spine precautions , an intubation while they are awake is often necessary. The first step is to numb the oropharynx with a local anesthetic. The use of 2% lidocaine sprayed into the patient's mouth and throat may cause the loss of a gag reflex and allow the patient to be awake during the procedure. In other situations, tracheal intubation either via the oral or nasal route should be performed when the patient is awake, using a fiberoptic scope. In this situation, facilitating fiberoptic intubation may require the blockade of specific nerves. Nerve Blocks In the mouth, sensation to the anterior aspect of the tongue is innervated by the lingual nerve. In contrast, the posterior third of the tongue and the oropharynx are innervated by the pharyngeal branches of the glossopharyngeal nerve (the ninth cranial nerve) and by the vagus nerve (the tenth cranial nerve). Spraying the oral cavity with a local anesthetic and asking the patient to gargle and swallow the anesthetic spray can easily anesthetize these nerves. Alternately, these nerves are easily blocked by a 2-mL bilateral injection of a local anesthetic into the base of the palatoglossal arch, using a 25-gauge spinal needle. The superior laryngeal nerve, a branch of the vagus nerve, innervates the inferior aspect of the larynx to the level of the vocal cords. This nerve can be blocked by placing gauze soaked with a local anesthetic in the pyriform sinuses. In addition, this nerve may be blocked externally by locating the hyoid bone and injecting 3 mL of 2% lidocaine 1 cm below each greater cornu, where the internal branch of the superior laryngeal nerves penetrates the thyrohyoid membrane . The recurrent laryngeal nerve innervates the mucosa below the vocal cords. This nerve may be blocked with a transtracheal injection of a local anesthetic. A transtracheal block is performed by identifying and penetrating the cricothyroid membrane while the neck is extended. The aspiration of air can confirm an intratracheal position; 4 mL of 4% lidocaine is then injected into the trachea at the end of an expiration. A deep inhalation and cough immediately following the injection distribute the anesthetic throughout the trachea. Using a local anesthetic to block the above nerves may facilitate an endotracheal intubation in a patient who is conscious by depressing both the protective cough reflex and the swallowing reflex. Special precautions should be taken with patients at high risk for aspiration. In some patients, the use of anesthesia may be limited to the nasal passages and may be administered with either a blind nasal intubation or a fiberoptic nasal intubation. Using local anesthetics in the nares protects the airways of patients who are at high risk for aspiration. Manual Ventilation After a patient has been administered anesthetic induction drugs and neuromuscular blockers and cannot be awakened, maintaining a patent airway and adequate ventilation can be challenging when a difficult airway is encountered . Mask ventilation does add air to the stomach and may predispose patients to vomit. This risk is significant in patients with acid reflux disease. If manual ventilation by mask is adequate, the patient can continue to be ventilated until he or she awakens and can be intubated by an alternate technique. In situations in which manual ventilation is difficulteven with the use of oral or nasal airwaysthen aggressive intervention may become necessary: a surgical airway may need to be created. The laryngeal mask airway is used when conventional methods of endotracheal intubation with a laryngoscope are unsuccessful and respiratory compromise is imminent. The laryngeal mask airway was designed as a compromise between the face mask and the endotracheal tube. It is used extensively throughout the world and has been included in the algorithm created by the American Society of Anesthesiologists to treat the difficult airway. This device requires no direct visualization of the vocal cords. However, a disadvantage of this device is that it does not prevent aspiration. Therefore, in patients who are at high risk for aspiration, a small endotracheal tube can be placed with fiberoptic guidance. Two new laryngeal mask airways have been introduced: the "fast-track" laryngeal mask airway and the ProSeal laryngeal mask airway. The fast-track laryngeal mask airway can be used much as the original laryngeal mask airway. The primary advantage of the fast-track device is that it allows endotracheal tube placement without direct laryngoscopy (Figure 46). The ProSeal device is very similar to the original laryngeal mask airway; however, it contains an extra lumen to suction the stomach and the intestinal contents. None of the three types of laryngeal mask airwars provide protection against aspiration in a patient who vomits. Esophageal-Tracheal Combitube The esophageal-tracheal Combitube is another device that can be used in emergency situations. The Combitube is a hybrid of the traditional endotracheal tube and the former esophageal obturator airway. This device can prevent aspiration because of the presence of a tracheal cuff (Figure 47). The GlideScope The GlideScope (Saturn Biomedical Systems, Inc., Burnaby, British Columbia) is a new video laryngoscope that can be a useful alternative to the conventional fiberoptic scope for placement of an endotracheal tube in the trachea when confronted with a difficult airway. The GlideScope has a high-resolution digital camera incorporated in the blade, which displays a view of the vocal cords on a monitor. The blade is fashioned after the Macintosh blade with a 60 curvature to match the anatomic alignment. The blade is made of a soft plastic material and has a thickness of 18 mm. The blade also has an embedded antifogging mechanism. The GlideScope can be used with minimal treatment of the oropharynx with local anesthetic and is useful for not only endotracheal intubation, but also as a diagnostic tool. | | Patient Preparation: Anesthesia & Surgery Preoperative Assessment Patients scheduled for surgery should have a preoperative evaluation by the surgeon and the anesthesiologist, especially if general anesthesia will be administered. These patients should have a baseline laboratory assessment, which should include a complete blood count. In patients with coexisting disease, an evaluation of other functions is necessary. Patients over the age of 50 and patients with heart disease should also have an electrocardiogram (ECG). A preoperative pulmonary function assessment in patients with pulmonary disease is also warranted. These tests may determine postoperative care requirements and assess whether preoperative treatment may reduce the perioperative risks. Therefore, in a high percentage of cases, a cardiac or pulmonary consultation is necessary in the preoperative assessment. Table 45 provides a list of tests with the sensitivity, specificity, and approximate cost of each. | Table 45. Tests Performed in the Preoperative Patient Evaluation.
| | | Test | Sensitivity (%) | Specificity (%) | Cost (Approximate) | | Ambulatory ECG (24 h) | 70 | 85 | $280 | | ECG (stress test) | 65 | 80 | $450 | | Stress echo | 80 | 85 | $600 | | Thallium (planar) | 90 | 80 | $1,200 | | Thallium (SPECT) | 90 | 90 | $1,200 | | Dipyridamole thallium | 90 | 90 | $1,200 | | Cardiac catheterization | 95 | 95 | $2,500 | |
| Tests for Patients with Cardiac Disease Electrocardiogram All patients over age 50 and patients with cardiac disease should have an ECG. A preoperative ECG can provide important information on the status of the patient's cardiac circulation. Patients with abnormal Q waves seen on their ECG suggest a past myocardial infarction. These patients may be at an increased risk of a perioperative cardiac event and may need further preoperative assessment. Approximately 30% of infarctions are silent and only detected on routine ECGs, most notably in patients with diabetes or hypertension. In addition to the ECG, history taking can provide important information about the patient's cardiac status. Assessing the patient's functional status by knowing the patient's exercise tolerance may determine the need for a cardiac evaluation. The information from cardiovascular testing may allow for optimizing preoperative medications, provide information on perioperative monitoring, or determine the need for coronary revascularization. 24-Hour Ambulatory ECG The 24-hour ambulatory ECG requires the placement of a Holter monitor, which records a continuous 12-lead ECG for 24 hours. This monitor detects arrhythmias and ischemic changes during a 24-hour period. This test often requires further testing, particularly if ischemic changes are noted. Exercise Stress Test In an exercise stress test, the patient exercises with ECG leads attached; the patient's heart rate and blood pressure are monitored. The test is considered positive if any of the following signs and symptoms are present: myocardial ischemia, patient complaints of chest pain or dyspnea, and clinical signs of left ventricular dysfunction. Even more significant is a decrease in the patient's blood pressure in response to exercise; this finding may be associated with global ventricular dysfunction. Syncope during the test also signifies decreased cardiac output. A positive exercise ECG stress test should alert the anesthesiologist that the patient is at risk for ischemia, within a wide range of heart rates, which may occur during surgery. These patients may require further workup and medical management. Thallium Exercise Test The sensitivity and specificity of a noninvasive stress test can be increased by nuclear imaging techniques. Thallium-201 (Tl-201) is a radioactive compound that mimics potassium uptake by viable myocardial cells . The sensitivity of exercise Tl-201 imaging depends on the imaging technique. For detecting coronary artery disease, qualitative visual Tl-201 imaging has an average sensitivity of 84% and a specificity of 87%, although these rates are improved with better imaging techniques. The drawback to T1-201 imaging is that patients have to remain stationary to avoid artifacts. Thallium defects are reported as normal, fixed, or reversible. Other important measures noted by stress Tl-201 imaging are the size of the defect, lung uptake, and left ventricular cavity size. A large lung uptake of isotope has been associated with myocardial ischemia; this ischemia produces left ventricular dysfunction, which may result in pulmonary edema. The presence of a distended left ventricular cavity on the immediate post-stress image is another marker of severe coronary artery disease, presumably as a result of myocardial ischemia. Coronary Testing with Pharmacologic Agents The use of pharmacologic agents to induce cardiac stress in patients who cannot exercise can also detect coronary artery disease. These agents can be divided into two categories: (1) those that result in coronary artery vasodilatation (eg, dipyridamole and adenosine) and (2) those that increase myocardial oxygen demand (eg, dobutamine and isoproterenol). Coronary artery vasodilators are useful for defining the potential risk of myocardial disease by causing differential flows in normal coronary arteries compared with arteries that have a stenosis. The use of dobutamine is an alternative method of increasing myocardial oxygen demand without exercise. The goal is to increase heart rate and blood pressure. Echocardiography The use of echocardiography for preoperative cardiac evaluation has increased in recent years. Echocardiography can evaluate left ventricular function, pulmonary vascular pressures, and valvular competence. In most cases, a transthoracic approach is used. Transesophageal echocardiography may provide more detailed measures of valvular abnormalities and left ventricular function. Echocardiography can also be performed with exercise. In patients who are unable to exercise, dobutamine has been used to mimic the stress effects of exercise. Coronary Angiography Coronary angiography has been called the gold standard for defining coronary anatomy. Angiography can assess valvular function and hemodynamic indices, including ventricular pressure and the gradients across valves . In most cases, angiography is performed after a positive stress test to determine whether coronary revascularization will both improve cardiac function and reduce perioperative cardiac morbidity after noncardiac surgery. One major difference between the stress tests and coronary angiography is that the latter provides the clinician with anatomic, not functional, information. However, it is an expensive test with potential complications. Tests for Patients with Pulmonary Disease Preoperative Pulmonary Evaluation Patients scheduled for head and neck surgery may present with coexisting pulmonary disease. The presence of pulmonary disease may increase perioperative morbidity and mortality. Patients with acute pulmonary disease who are scheduled for elective surgery may choose to postpone the surgery until the pulmonary disease resolves. Patients with chronic pulmonary disease may benefit from a preoperative pulmonary workup that includes a measure of arterial blood gases, a chest x-ray, and pulmonary function tests. Pulmonary Function Tests Preoperative pulmonary function tests (1) measure the severity of lung disease, (2) measure the efficacy of bronchodilator therapy (to improve pulmonary function), and (3) can predict the need for postoperative mechanical ventilation. Pulmonary disease may be classified as obstructive or restrictive . Obstructive Pulmonary Diseases Obstructive pulmonary disease includes asthma, emphysema, chronic bronchitis, bronchiectasis, and bronchiolitis. These disorders are characterized by an increase in expiratory airflow resistance that results in varying degrees of labored breathing. The most typical finding of pulmonary function tests is that both the forced expiratory volume per second (FEV 1 ) and the ratio of forced expiratory volume to forced vital capacity (FEV 1 /FVC) are less than 70% of the predicted values. The expiratory airflow resistance results in air trapping. In addition, the residual volume (RV) and total lung capacity (TLC) are increased. Wheezing is a common clinical finding and represents turbulent airflow. In mild obstructive disease, wheezing may be absent but can be elicited by prolonged exhalation. Restrictive Pulmonary Diseases Restrictive lung diseases may be either acute or chronic intrinsic disorders and include pulmonary edema, acute respiratory distress syndrome (ARDS), infectious pneumonia, and interstitial lung diseases. Restrictive pulmonary disease may also represent extrinsic disorders involving the pleura , the chest wall, the diaphragm, and neuromuscular function. Restrictive pulmonary disease is marked by decreased lung compliance that increases the work of breathing due to a characteristic rapid- shallow breathing pattern. Lung volumes are typically reduced, as are the FEV 1 and the FVC; however, the FEV 1 /FVC ratio is normal. The expiratory flow rates are unchanged. | | Special Surgical Considerations Surgery of the Oral Cavity & Airway Tonsillectomy & Adenoidectomy Preoperative Considerations Obstructive Sleep Apnea Most patients who undergo tonsillectomy and adenoidectomy are young and healthy . A few present with symptoms of obstructive sleep apnea. Patients with obstructive sleep apnea are often obese and may have potentially difficult airways. They may have short, thick necks, large tongues , and redundant pharyngeal tissue; the latter may require the patients to be awake during endotracheal intubation. Sedative premedication may be avoided in children with obstructive sleep apnea, intermittent obstruction, or very large tonsils. Upper Respiratory Tract Infections Patients may present with upper respiratory tract infections. Surgery for these patients should be postponed until the infection is resolved, usually 714 days. These patients may develop a laryngospasm with airway manipulation. This complication carries the potential for significant morbidity and even mortality. Intraoperative Considerations In some patients, endotracheal intubation may be significantly difficult; therefore, the presence of an otolaryngologist may be helpful at the time of intubation. The use of an oral RAE tube for endotracheal intubation may optimize visualization of the surgical field. In younger children in whom an uncuffed tracheal tube is used, in order to avoid inhalation blood from the pharynx area, the supraglottic area may be packed with a petroleum gauze tube provided an appropriate leak around the endotracheal tube is obtained. Patients should be awake when they are extubated, after protective airway reflexes have returned. In patients with reactive airway disease, including asthma, deep extubation may be warranted to prevent airway reactivity complications such as bronchospasm and laryngospasm. Postoperative Complications Throat Pack Retention and Pulmonary Edema Retention of the throat pack is one complication of tonsillectomies and adenoidectomies. Another complication is acute airway obstruction, such as a laryngospasm, which can lead to pulmonary edema. This edema occurs when the patient breathes against a closed glottis, creating a negative intrathoracic pressure. This pressure is transmitted to the interstitial tissue, increasing the hydrostatic pressure gradient and enhancing fluid out of the pulmonary circulation into the alveoli. Hemorrhage Hemorrhage may result from a bleeding tonsil. Reintubations often may be difficult. Care should be taken not to oversedate the patient, who may aspirate large quantities of blood. If the bleeding is not controlled, then the patient should be returned to the operating room for exploration and surgical hemostasis . Laser Surgery of the Airway Laser surgery for lesions in the airway (1) provides precision in targeting lesions, (2) minimizes bleeding and edema, (3) preserves the surrounding structures, and (4) provides rapid healing. The carbon dioxide laser has particular application in treating laryngeal or vocal cord papillomas, treating laryngeal webs, resecting redundant subglottic tissue, and treating hemangioma coagulation . Preoperative Considerations The appropriate preoperative equipment should include a laser-resistant endotracheal tube; other endotracheal tubes should be available for emergency situations. Anesthesia during laser surgery may be administered with or without an endotracheal tube. All standard PVC endotracheal tubes are flammable and can ignite and vaporize when they come in contact with the laser beam. Some surgeons may prefer using a Dedo or Marshall laryngoscope and intermittent ventilation with a Sanders ventilator. The Sanders ventilator is a jet ventilator that delivers oxygen at < 50 psi directly through a port in the laryngoscope. Intraoperative Considerations The patient's eyes must be protected by taping them shut, followed by the application of wet gauze pads and a metal shield to prevent laser penetration of the eyes. All operating room personnel should wear special protective glasses . Airway fires are a risk with laser surgery. A plan to handle a fire, if one occurs, is necessary. In some centers, the tracheal balloon is filled with blue methylene gas; therefore, rupture of the balloon is an early indication of a hazard . Both oxygen and nitrous oxide support combustion and a mixture of 30% oxygen and nitrogen may be used. If a fire occurs, ventilation should be discontinued, oxygen turned off, and the endotracheal tube removed. If the flame persists, the field should be flooded with normal saline. A direct examination of the pharynx and larynx provides information about the extent of the burn. If a Dedo or Marshall laryngoscope is used, maintenance anesthesia should be administered with an intravenous anesthetic to prevent inadvertently anesthetizing the surgeon and other surgical staff. The patient should be reintubated with a regular endotracheal tube after the bronchoscope is removed. The use of the Sander's jet ventilator is contraindicated; it is associated with the risk of pneumothorax and pneumomediastinum due to the rupture of either alveolar blebs or a bronchus. Postoperative Considerations In the event of an airway fire during surgery, the patient should be monitored for at least 24 hours. Steroids and antibiotics should be considered for severe burns. If respiratory problems are encountered, then the patient should be observed in an intensive care setting. Surgery of Patients with Acute Epiglottitis Acute epiglottitis is an infectious disease caused by Haemophilus influenzae B. It can progress rapidly from sore throat to airway obstruction to respiratory failure and death if the proper diagnosis and treatment are delayed. Patients are usually between the ages of 2 and 7, although acute epiglottitis has been reported in children younger than age 2; it has also been reported in adults. Characteristic signs and symptoms of acute epiglottitis include the following: the sudden onset of fever ; dysphagia; drooling; thick, muffled voice; and a preference for the sitting position, leaning forward and with the head extended. Retractions, labored breathing, and cyanosis may be observed in cases where respiratory obstruction is present. Preoperative Considerations Direct visualization of the epiglottis should not be attempted in a patient who is not anesthetizedit could lead to airway compromise and death. The patient should be kept calm, since agitation is likely to have an adverse effect on the patient's respiratory abilities . The differential resulting from negative pressure inside and atmospheric pressure outside the extrathoracic airway results in a slight narrowing during normal inspiration. In a patient with airway obstruction, the pressure differential is exaggerated during inspiration. The likely collapse of the airway may become life threatening in the struggling and agitated patient. Intraoperative Considerations The intraoperative considerations for patients with acute epiglottitis include the following steps: (1) securing the airway; (2) inducing anesthesia with halothane or sevoflurane while maintaining spontaneous ventilation; (3) having an emergency airway cart and tracheostomy tray available and open; and (4) if the patient is a child, allowing his or her parent into the operating room to help keep the patient calm. Postoperative Considerations Postoperative care should be handled in the intensive care unit for continued observation and radiographic confirmation of tube placement. Tracheal extubation is usually attempted 4872 hours after a significant leak around the endotracheal tube is present. At the same time, visual inspection of the larynx by flexible fiberoptic bronchoscopy can confirm a reduction in swelling of the epiglottis and surrounding tissues. Parotid Gland Surgery Parotid gland surgery is usually performed for tumors but it can also be performed for infectious disorders. Some diseases of the parotid gland have been associated with alcohol use; these patients may exhibit the signs and symptoms of alcohol-related diseases. Parotid gland surgery is performed under general anesthesia. In most cases, the facial nerve needs to be preserved and nerve monitoring is therefore necessary. When a radical parotidectomy is performed, the facial nerve may be sacrificed and reconstructed with a graft from the contralateral greater auricular nerve. Muscle relaxants should be avoided if nerve monitoring is used. In addition, nasal intubation may be necessary if the mandible has to be dislocated. Nasal Surgery A significant percentage of nasal surgery is performed to improve cosmesis, although a large percentage is performed for functional restoration of the airway. Functional restoration is usually performed for either congenital or post-traumatic deviations of the septum. Nasal surgery is office based and performed with local anesthesia and intravenous sedation. It is important to note that patients with nasal polyps and asthma often have a hypersensitivity to aspirin, which can precipitate bronchospasm. Intraoperative & Postoperative Considerations The most important consideration of nasal surgery is achieving profound vasoconstriction in the nares to minimize and control bleeding. This vasoconstriction can be achieved with cocaine packs , local anesthetics, and epinephrine infiltration. Since these drugs have a profound effect on the cardiovascular system, a careful evaluation of the patient's cardiovascular functioning is essential, especially for older patients or patients with known cardiac disease. A vasoconstrictor can also precipitate dysrhythmias. A moderate degree of controlled hypotension combined with head elevation decreases bleeding in the surgical site. Blood may passively enter the stomach. Placing an oropharyngeal pack or suctioning the stomach at the conclusion of surgery may attenuate postoperative retching and vomiting. Ear Surgery The ear and its associated structures are target organs for many pathologic conditions. One of the most common ear surgeries is the placement of myringotomy tubes; tympanoplasties and the placement of cochlear implants are also common procedures. The surgeries usually require general anesthesia and in some cases rely on neuromonitoring. When nerve monitoring is undertaken, muscle relaxants should not be used. Patients are often nauseous as a result of surgery; therefore, adequate pretreatment with antiemetics and the use of anesthetics such as propofol and sevoflurane can reduce the incidence of nausea and vomiting. For myringotomies and tube insertions, anesthetic premedication is not recommended because most sedative drugs far outlast the duration of the surgical procedure. Anesthesia may effectively be accomplished with a potent inhalation drug, oxygen, and N 2 O administered by mask. As with other ear surgeries, the patient should be pretreated for nausea and vomiting. Middle Ear & Mastoid Surgery Tympanoplasty and mastoidectomy are two of the most common procedures performed on the middle ear and accessory structures. To avoid intrusion into the surgical field, an oral or nasal RAE endotracheal tube may be considered. Although not totally contraindicated, N 2 O should be discontinued at least 30 minutes before placement of a tympanic membrane graft to avoid pressure-related displacement. In addition, extubation should be smooth to avoid straining, which may unseat the tympanic membrane graft or disrupt other repairs . Postoperative nausea and vomiting are the most common postoperative problems. They can be reduced by (1) decompressing the stomach after inducing general anesthesia, thereby emptying the stomach of gas and fluid; (2) limiting the use of opioids; and (3) using antiemetics. Neck Surgery Neck dissection may be complete, modified, or functional. The sternocleidomastoid muscle is the primary muscle involved. The primary nerve is the accessory or spinal nerve (CN XI), and the primary vascular structures are the internal and external jugular veins and the carotid artery. Often a neck dissection is performed to remove a tumor and may also involve a partial or total glossectomy. Preoperative Considerations Patients who present with tumors in this area may have a history of tobacco use and pulmonary disease and may need a preoperative pulmonary workup. In a large percentage of cases, the dissection may be bilateral and a tracheostomy may be performed to maintain a patent airway. Intraoperative Considerations Patients who undergo neck surgery may be a challenge to intubate if they have either a history of radiation treatment to the larynx and pharynx or a significant mass in the oral cavity. If nerve monitoring is undertaken, muscle relaxants should be avoided. Dissection around the carotid bulb may precipitate bradycardia, which may be treated with either an injection of a local anesthetic into the bulb or intravenous atropine or glycopyrrolate. Laryngeal edema can be a significant problem if no drains are placed. Postoperative Considerations Nerves injured in neck surgery can include the facial nerve, resulting in a facial droop. Injury to the recurrent laryngeal nerve can cause vocal cord dysfunction; if this injury is bilateral, airway problems may result. Since the phrenic nerve also traverses through the operative field, paralysis of the hemidiaphragm can occur if this nerve is injured. If injury to the phrenic nerve is bilateral, breathing will be impaired. With a low neck dissection, pneumothorax can occur. In addition, excessive coughing or agitation can result in hematoma formation and airway compromise. Al-Shaikh B, Stacey S. Essentials of Anaesthetic Equipment, 2nd ed. Philadelphia: Churchill Livingstone, 2002.
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| Miller RD. Miller's Anesthesia, 6th ed. Philadelphia: Churchill Livingstone, 2005.
| Morgan CE Jr, Mikhail MS, Murray MJ, Larson CP Jr. Clinical Anesthesiology, 4th ed. New York: McGraw-Hill Medical, 2005.
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